Is there a quick way to dim the brightness on a fluorescent display? In may case, a late 1980s vintage CD player. It has just the factory setting, which is a bit too much.
I would not mind, say, a variable pot, or a two- or three-position switch, or even just turning it off as in the case of some purist audiophile gear.
As I recall, FTD ( fl) displays run on AC at roughly 30 vac.
I would not mind, say, a variable pot, or a two- or three-position switch, or even just turning it off as in the case of some purist audiophile gear.
As I recall, FTD ( fl) displays run on AC at roughly 30 vac.
Put a sticker of the material used for windows, it is an adhesive tinted film..
The performance will be spoiled if you change the supply voltage, as it is they are obsolete.
The performance will be spoiled if you change the supply voltage, as it is they are obsolete.
The mains transformer for my CDP has dedicated windings for the FTD supply. It's not even regulated.
I think fluorescent displays went out of production because they were fragile, and short lived compared to LEDs, and later LCDs. And their power supply was an issue.
I suggest you read up about this before trying to modify the unit, as the voltage vs. current curves for fluorescent lamps have a sweet spot, if you go away from those specified levels the light output and life are badly affected.
I suggest you read up about this before trying to modify the unit, as the voltage vs. current curves for fluorescent lamps have a sweet spot, if you go away from those specified levels the light output and life are badly affected.
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I've never needed to do it or seen it done the way below but it's probably worth trying.
By manipulating the cathode bias voltage and in turn the anode current, the brightness could be altered. The attached is the power supply part of AKAI CD73. The F-F on the left is the filament winding from the power transformer that drives the filament, or cathode, of the VFD. D1, a zener diode, biases the cathode at about 9V above the grid supply voltage. By changing D1 to 12V, 15V or so on, the grid would be at a less positive potential against that of the cathode, hopefully allowing less current to flow.
AKAI CD73 generates its -37V VFD grid supply with a doubling rectifier and a simple regulator, yours may differ. But I guess the cathode biasing scheme would be more similar than different.
By manipulating the cathode bias voltage and in turn the anode current, the brightness could be altered. The attached is the power supply part of AKAI CD73. The F-F on the left is the filament winding from the power transformer that drives the filament, or cathode, of the VFD. D1, a zener diode, biases the cathode at about 9V above the grid supply voltage. By changing D1 to 12V, 15V or so on, the grid would be at a less positive potential against that of the cathode, hopefully allowing less current to flow.
AKAI CD73 generates its -37V VFD grid supply with a doubling rectifier and a simple regulator, yours may differ. But I guess the cathode biasing scheme would be more similar than different.
It's a common design to set the VFD brightness at the cathode, regardless make or year. I would go after the filament supply, find that zener, and start tweaking away. If you don't feel comfortable tracing a schematic out of an actual PCB assembly, a service manual probably could be found at hi-fi engine or other manual sites.
That pot would then become a self-bias resistor. Probable problem with that is the brightness of an active digit would vary by its content, resulting in uneven digit-to-digit brightness across the screen. I think that is why a zener was used in the first place.
I thought the zener was for the whole display, and the pot would allow you to change the voltage by changing the voltage fed to the zener, easier than swapping zeners.
Not a good idea, it seems.
Not a good idea, it seems.
"swapping" the zeners isn't less easy than a pot in this case. The zener of the highest voltage could be left in circuit, and one or more lower voltage zeners be switched in with a single pole, multi throw switch, bypassing the highest zener.
A foolproof method is to vary the filament voltage, thus lowering heater temperature and emission.
Filament voltage in a VFD is usually rated for the balance of sufficient thermal electron emission from the cathode (the filament) and the long life of the filament itself. In other words, at the rated filament voltage the thermal electron emission is just above the sufficient level in order to maintain display quality, or lowing the filament voltage may risk display quality.